Known rubber materials for automotive tires include a conjugated diene-based rubber (e.g., a styrene-butadiene copolymer) prepared through an emulsion polymerization process or a solution polymerization process. Demanded rubber materials for tires include a conjugated diene-based rubber capable of producing a tire that exhibits low rolling resistance and is excellent in terms of various properties, including wear resistance, fracture properties, and steering stability. In connection therewith, a variety of techniques have been proposed for modifying conjugated diene-based rubbers used for tires (refer to, for example, Patent Documents 1 to 3).
Patent Document 1 discloses a method for producing a conjugated diene-based polymer having a primary amino group and an alkoxysilyl group at a terminal of the polymer by reacting a conjugated diene-based polymer having a polymerization active terminal with a modifying agent (i.e., an alkoxysilane compound having a nitrogen-containing group prepared through protection of active hydrogen of an amino group with a silyl group), followed by hydrolysis. Patent Document 2 discloses a method for modifying a conjugated diene-based polymer by use of N-n-butyl-aza-2,2-dialkoxysilacyclopentane. Patent Document 3 discloses a method for producing a modified conjugated diene-based polymer through a step of reacting the active terminal of a conjugated diene-based polymer having a molecular weight distribution within a specific range with a modifying agent containing four or more alkoxy groups bonded to a silyl group and one or more nitrogen atoms, and a step of reacting the active terminal with a modifying agent containing two or three alkoxy groups bonded to a silyl group and one or more nitrogen atoms.